fixing error wheen raising an error 500 that uses simple_message_page WITHOUT...

fixing error wheen raising an error 500 that uses simple_message_page WITHOUT having called context processor, by default using "basetheme_bootstrap/base4.html"

basetheme_bootstrap/templates/basetheme_bootstrap/simple_message_page.html

-{% extends basetheme_bootstrap_base_template %}
+{% extends basetheme_bootstrap_base_template|default:"basetheme_bootstrap/base4.html" %}
 {% load i18n %}
 
 {% block whole_content_page_title %}